The central objective of this research is to determine neuroanatomic relationships among neurons having known chemical characteristics, especially those substances important for interneuronal communication processes, with particular emphasis on cholinergic and monoaminergic histochemistry in the substantia nigra and neostriatum. We have developed a pharmaco-histochemical regimen for acetylcholinesterase (AChE,EC 3.1.1.7), which, compared to previous protocols for the enzyme, permits improved visualization of AChE neuronal somata and their processes in the central nervous system. Furthermore, we have developed histochemical and histologic methods for the demonstration of the same brain section of AChE, catecholamines, and a variety of substances that can be labelled radioactively, including 3H-proline for the demonstration of neuroanatomic pathways in the brain and 3H-quinuclidinyl benzilate and 125I-alpha-bungarotoxin for the apparent demonstration of muscarinic and nicotinic receptors, respectively. In addition, we have recently synthesized a compound that interacts selectively and irreversibly with high affinity uptake mechanisms of cholinergic neurons and hence should be useful in histologically demonstrating those neurons. In this renewal application I propose continuing and extending this work by (1) making a detailed cytoarchitectural comparison of dopamine and AChE-containing neurons in the substantia nigra, (2) examining neuroanatomic relationships among the various afferents to AChE interneurons in the neostriatum (caudate-putamen complex), (3) examining the possible histologic presence of nicotinic and muscarinic receptors on dopamine terminals in the neostriatum and the possible localization of acetylcholine and other cholinergic substances within those dopamine terminals, and (4) developing a method for cholinergic neurons based on high affinity uptake mechanisms. It is hoped that this research will shed light on basic brain mechanisms and brain mechanisms as they relate to cholinergic-monoaminergic interactions in Parkinsonism, tardive dyskinesias, Huntington's disease, and other forms of chorea.